资源环境科技发展态势分析平台

Using Van Allen Probes pitch angle-resolved electron flux data, we report intriguing events of electron butterfly pitch angle distributions (PADs) at L > similar to 5.5 on the nightside with distinct durations, i.e., about 9 hr for the 28-29 April 2013 event and over 2 days for the 2-5 May 2013 event. The formation and evolution of the short-duration electron butterfly PADs exhibited insignificant dependence on electron energy, probably resulting from a combination of drift shell splitting, magnetopause shadowing, and wave diffusion, but the long-duration electron butterfly evolution presented strong energy dependence, likely mainly attributed to interactions with MS waves. Both the short-duration and long-duration electron butterfly PADs disappeared closely related to enhanced substorm activities, while the responsible waves could be plasmaspheric hiss or chorus waves. Our results demonstrate that radiation belt electron butterfly PADs are naturally complex in both spatial and temporal scales and well connected to solar wind condition, substorm activity, and magnetospheric wave distribution.

Plain Language Summary Due to dynamic variations of magnetospheric physical processes, radiation belt electrons show different kinds of pitch angle distributions (PADs). Among them, butterfly PADs, recognized as a local flux minimum at 90 degrees pitch angle, have received intensive attention but remain not fully understood yet. The contributing mechanisms include drift shell splitting, magnetopause shadowing and associated outward radial diffusion, and wave-particle interactions. Using high-quality Van Allen Probes Magnetic Electron Ion Spectrometer, Relativistic Electron-Proton Telescope, and Electric and Magnetic Field Instruments Suite and Integrated Science data sets, we register two interesting events of electron butterfly PADs at L > similar to 5.5 on the nightside with very distinct evolution profiles both in time and energy, i.e., similar to 9 hr duration with insignificant energy dependence for the 28-29 April 2013 event and over 2-day duration with strong energy dependence for the 2-5 May 2013 event. Detailed analyses indicate that while the short-duration butterfly PADs probably result from a combination of drift shell splitting, magnetopause shadowing, and wave diffusion, the long-duration butterfly PADs are likely to be mainly caused by interactions with MS waves. Our study therefore reports the natural complexity of outer zone electron butterfly PADs in both spatial and temporal scales and furthers current understanding of their connection with solar wind condition, substorm activity, and magnetospheric wave distribution.